Identification of the mechanisms by which age alters the mechanosensitivity of mesenchymal stromal cells on substrates of differing stiffness: Implications for osteogenesis and angiogenesis.

In order to identify the mechanisms by which skeletal maturity alters the mechanosensitivity of mesenchymal stromal cells (MSCs) and, the implications for osteogenesis and angiogenesis during bone formation, we compared the response of MSCs derived from children and skeletally-mature healthy adults cultured on soft and stiff collagen-coated polyacrylamide substrates. MSCs from children were more mechanosensitive, showing enhanced angiogenesis and osteogenesis on stiff substrates as indicated by increased endothelial tubule formation, PGF production, nuclear-translocation of YAP, ALP activity and mineralisation. To examine these mechanisms in more detail, a customised PCR array identified an age-dependent, stiffness-induced upregulation of NOX1, VEGFR1, VEGFR2, WIF1 and, of particular interest, JNK3 in cells from children compared to adults. When JNK3 activity was inhibited, a reduction in stiffness-induced driven osteogenesis was observed - suggesting that JNK3 might serve as a novel target for recapitulating the enhanced regenerative potential of children in adults suffering from bone degeneration. STATEMENT OF SIGNIFICANCE: We investigated the age-associated changes in the capacity of MSCs for bone regeneration involving the mechanosensitive signalling pathways, which reduce the ability of adult cells to respond to biophysical cues in comparison to cells from children, who are still undergoing bone development. Our results offer new insights into the mechanobiology of MSCs and sheds new light on age-altered mechanosensitivity and, on why children have such an immense capacity to regenerate their skeletal system. We have identified the mechanisms by which skeletal maturity alters the mechanosensitivity of mesenchymal stromal cells and an age-dependent, stiffness-induced upregulation of a number of prominent genes including, most notably, JNK3 in children cells, thus suggesting its potential to promote enhanced bone repair.